The present invention concerns methods for testing the operativeness of certain types of control systems. Control systems of the type here in question are provided with a feedback transducer for sensing the value of a monitored variable, a control device and actuatable adjuster units, the control device being provided with a self-monitoring circuit operative, when the control device is switched on, for implementing a testing program comprised of a sequence of test functions of operations devised to test the operativeness of the entire negative-feedback control system. In the event that the negative-feedback control system, as a result of the test program runthrough, is found to be inoperative or malfunctioning in any tested respect, the control device of the system is shut off and a malfunction indication is generated.
Such negative-feedback control systems are used, for example, in the context of anti-wheel-lock control in automotive braking systems. Such anti-wheel-lock systems are often provided with a built-in self-monitoring circuit. At the start of a trip, for example as the driver turns on the vehicle's engine, the self-monitoring circuit initiates a sequence of tests in accordance with a predetermined test program. If as a result of the test program the self-monitoring circuit ascertains that there is a malfunction in any tested part of the control system, a warning signal is triggered informing the user of the fact, e.g., a dashboard lamp becoming illuminated. This serves to inform the user that the anti-lock system has been shut off, and that he is not to rely on it during any possible hard braking.
Hard-braking contexts are hazardous by definition, and it is important that a driver know whether the anti-wheel-lock action afforded by his braking system is or is not operative, when commencing to brake very hard. A problem with systems of the type just outlined, is that the self-monitoring circuit itself may be inoperative or improperly functioning, so that despite inoperativeness of the anti-wheel-lock system, the user is not informed of the situation.